1. Liz Chapman, PhD, Geochemist ECHELON Applied Geosciences 1 © Copyright 2014 EchelonAGC

2.  For a variety of fluids (fresh water, brines, AMD-impacted and co- produced waters)  And many geologic rock types and materials  Coal, shale, permeable limestone and sandstone aquifers  Deep and shallow units  Cements/grouts/combustion byproducts (coal fly ash)  Must be able to identify contaminant source as well as provide ongoing monitoring  Introduced tracers  Major and trace element geochemical signatures  Natural isotopic signatures © Copyright 2014 EchelonAGC

3.  Four naturally-occurring stable isotopes, including 87 Sr and 86 Sr  87 Sr is supplemented by the slow decay of 87 Rb (‘radiogenic isotope’)  Half-life: 48.8 Ga  87 Sr/ 86 Sr increases with time © Copyright 2014 EchelonAGC Capo et al., 1998

4.  Rocks with different compositions and geological histories develop distinct 87 Sr/ 86 Sr ratios  Reflect sources of Sr available during formation  Waters which interact with these units can inherit their 87 Sr/ 86 Sr  87 Sr/ 86 Sr in geologic materials is an indicator of both age and geochemical origin © Copyright 2014 EchelonAGC

5.  Systematics understood  Ubiquitous and abundant  One of the most abundant trace elements in crustal rocks  Proxy for calcium  Does not fractionate appreciably during physical, chemical, or biological processes © Copyright 2014 EchelonAGC

7.  Marcellus produced waters Four Pennsylvania counties Bradford Westmoreland Washington Greene Different sample types: Individual well single samples Impoundment samples Produced water time series © Copyright 2014 EchelonAGC Chapman et al., 2012; Kolesar et al., 2013; Capo et al., 2014

8. 0 4 8 12 16 2 6 14 10 20304050 Sr SW  Bradford Co. Washington Co. Greene Co. Westmoreland Co. n 0.7100.7110.712 87 Sr/ 86 Sr © Copyright 2014 EchelonAGC Chapman et al., 2012

9. © Copyright 2014 EchelonAGC Capo et al., 2014

10. © Copyright 2014 EchelonAGC  Determination of origin of dissolved constituents in surface and ground waters affected by multiple sources  Quantification of mixing  Extremely sensitive tracking

11.  Greene County site with:  Six Marcellus laterals  One vertical Marcellus well  Five Upper Devonian (UD) gas wells  One shallow groundwater spring  Sr measured before and after hydraulic fracturing of laterals © Copyright 2014 EchelonAGC Kolesar Kohl et al., 2014

12. © Copyright 2014 EchelonAGC

13.  Most UD wells show no change after fracturing (p values >0.05)  For isotopic shifts to be considered significant enough to suggest Marcellus fluid incursion,  Sr would need to decrease by 1-3 units Kolesar Kohl et al., 2014

14. © Copyright 2014 EchelonAGC  Sr isotope values fall between Marcellus and Upper Devonian values  Values shift on a semiannual basis (±0.8 from the mean)  Spring water contains very little Sr  Very sensitive to any potential mixing with produced water Kolesar Kohl et al., 2014

15. © Copyright 2014 EchelonAGC  The only well in the study that showed a significant change in Sr isotope values after horizontal wells were fractured (from +33.8 to +35.9)  Sr concentration also increased by ~200 mg/L  New pathways within the Marcellus were opened up by fracturing Kolesar Kohl et al., 2014

16. © Copyright 2014 EchelonAGC  Calculated mixing models between produced waters and spring water  Most sensitive elements: Ba, Br, Cl, Sr  Elemental ratios (Sr/Ca, Br/Cl) less sensitive than absolute concentrations Kolesar Kohl et al., 2014

17. © Copyright 2014 EchelonAGC  Greater sensitivity than elemental conc., especially in waters with natural seasonal variation  Unlike elemental concentration, Sr isotopes can distinguish between UD and Marcellus produced waters Kolesar Kohl et al., 2014

18. © Copyright 2014 EchelonAGC  Subsequent to hydraulic fracturing, no significant migration of Marcellus-derived fluids was observed in Upper Devonian or shallow groundwater units  Shift in Sr isotopes of vertical Marcellus well suggests fracturing opened new flowpaths within the unit  Sr isotopes show greater sensitivity to potential brine migration than elemental concentrations or ratios

19.  Capo, R.C., Stewart, B.W., Rowan, E., Kolesar, C., Wall, A.J., Chapman, E.C., Hammack, R.W., and Schroeder, K.T., 2014. The strontium isotopic evolution of Marcellus Formation produced waters, southwestern Pennsylvania. International Journal of Coal Geology, available online 28 Dec 2013.  Capo, R.C., Stewart, B.W., and Chadwick, O.A., 1998. Strontium isotopes as tracers of ecosystem processes: theory and methods. Geoderma, v. 82, p. 197-225.  Chapman, E.C., Capo, R.C., Stewart, B.W., Kirby, C.S., Hammack, R.W., Schroeder, K.T., and Edenborn, H.M., 2012. Geochemical and strontium isotope characterization of produced waters from Marcellus Shale natural gas extraction. Environmental Science & Technology, v. 46, p. 3545-3553.  Kolesar Kohl, C.A., Capo, R.C., Stewart, B.W., Wall, A.J., Schroeder, K.T., Hammack, R.W., and Guthrie, G.D., 2014. Strontium isotopes test long-term zonal isolation of injected and Marcellus Formation water after hydraulic fracturing. Environmental Science & Technology, v. 48, p. 9867-9873.  Kolesar, C.A., Capo R.C., Wall, A.J., Stewart, B.W., Schroeder, K.T., Hammack, R.W., 2013. Using strontium isotopes to test stratigraphic isolation of injected and formation waters during hydraulic fracturing, AAPG Search and Discovery Article #90163. © Copyright 2014 EchelonAGC

20.  University of Pittsburgh: Rosemary Capo, Brian Stewart, Courtney Kohl, Andrew Wall, James Gardiner  Department of Energy: Karl Schoeder, Rick Hammack, Hank Edenborn 20 © Copyright 2014 EchelonAGC